Stable cosmetic ink composition

ABSTRACT

A cosmetic ink composition comprises a particulate material, a (meth)acrylic acid homopolymer or salt thereof, and a rheology modifier. The particulate material can have a Particle Size Distribution D50 of about 100 nm to about 2,000 nm. The (meth)acrylic acid homopolymer or salt thereof can have a weight average molecular weight of less than about 20,000 daltons. The rheology modifier can be selected from the group consisting of alkali swellable emulsion polymers, hydrophobically modified alkali swellable emulsion polymers, and combinations thereof. The cosmetic ink composition can have a first dynamic viscosity of greater than about 1,100 cP at a shear rate of 0.1 sec−1 measured at 25° C. and a second dynamic viscosity of less than about 100 cP at a shear rate of 1,000 sec−1 measured at 25° C.

FIELD OF THE INVENTION

Described herein is an ink composition for inkjet printing applications, and more particularly a cosmetic ink composition comprising a particulate material that exhibits long-term stability while still being suitable for high frequency printing via thermal and/or piezo inkjet printheads.

BACKGROUND OF THE INVENTION

Most printing applications are designed for printing onto white substrates for document production or photo printing. For such applications, black inks are primarily used in combination with three or more colored inks. Formulating stable black inks and colored inks is well understood. For instance, it is known that molecular dyes will generally not exhibit settling over time if they are soluble in the carrier. In addition, pigment-based black inks generally utilize particle sizes small enough to be suspended in low viscosity carriers and take advantage of both Stokes' Law and Brownian motion to keep the particles suspended. However, these inks exhibit very low opacity, as dyes are transparent by nature and pigmented-based black inks use particle sizes that are small enough to be suspended but are much smaller than the particle sizes required to scatter visible light. For opacifying purposes, optimal light scattering occurs at half the wavelength of light. Since the visible light spectrum ranges from about 400 to about 700 nm, the optimal particle size for opacification is from about 200 to about 350 nm. This is significantly larger than the particle size of stable black pigment-based inks used in consumer printing applications which generally comprise particles that are less than about 50 nm in size.

For cosmetic printing applications, it is known that the ink must be sufficiently opaque to cover and/or hide skin imperfections. However, it is difficult to formulate an opaque stable ink which can be jetted due to the particle size and levels needed to achieve opacity and the gravitational settlement of the large and/or dense particles used to create such inks. In particular, it is challenging to formulate a stable ink comprising titanium dioxide, a commonly used white pigment, that is substantially free of particle settling over the shelf-life of the product. While there are multiple industries that routinely use titanium oxides in products which can demonstrate long-term stability, these products generally have very high viscosities. For instance, sunscreens and traditional makeups and/or skin care products which are applied manually comprise titanium oxide particles and are stable; however, they are only able to do so through viscosities that are orders of magnitude greater than the viscosity of typical inkjet compositions and are not compatible with inkjet printers and/or cartridges.

For many years, the inkjet printing industry has attempted to create stable white inks that can exhibit high frequency jetting, nozzle health, and/or drop placement accuracy. Current formulations utilize rheology modifiers and/or particle surface treatments to help slow the settling rate of the particles. However, the time frame of the particle suspension in such formulations is only on the order of days or weeks. This can be helpful for industrial applications where the printer operator only needs to re-suspend the particles through agitation every few days, rather than every few hours. However, this does not enable a product to be sold to a consumer in a typical retail environment where the product may need to be stable for months or years as it passes through a supply chain and is used by a consumer. Other formulation approaches have utilized titanium oxides with a smaller particle size to slow the rate of settling and/or have employed secondary particles such as hollow spheres to help provide some opacity. However, such formulations still settle within weeks, and the opacity is much lower than that of inks which use titanium oxides with particle sizes of 200 nm or greater. Even the most stable current white inks demonstrate particle settling over time if left undisturbed. Manufacturers of such inks recommend vigorous shaking on a daily or weekly basis to redisperse the particles and/or recommend that these inks are recirculated during use.

As such, there is a need for an opaque inkjet ink composition with increased particle suspension stability for consumer cosmetic applications. In particular, there is a need for a cosmetic ink composition that comprises particles that are big enough to create opacity yet remain in suspension and has a viscosity that is compatible with inkjet printer cartridges and nozzle technology.

SUMMARY OF THE INVENTION

A cosmetic ink composition comprises: (a) a particulate material having a Particle Size Distribution D50 of from about 100 nm to about 2,000 nm; (b) a (meth)acrylic acid homopolymer or a salt thereof having a weight average molecular weight of less than about 20,000 daltons; and (c) a rheology modifier, wherein the rheology modifier is selected from the group consisting of alkali swellable emulsion polymers, hydrophobically modified alkali swellable emulsion polymers, and combinations thereof; wherein the cosmetic ink composition has a first dynamic viscosity of greater than about 1,100 cP at a shear rate of 0.1 sec⁻¹ measured at 25° C. and a second dynamic viscosity of less than about 100 cP at a shear rate of 1,000 sec⁻¹ measured at 25° C.

A cosmetic ink composition comprises: (a) from about 1 to about 30 active weight (wt) % of a particulate material; (b) a (meth)acrylic acid homopolymer or a salt thereof; and (c) from about 0.3 to about 1 active wt % of a rheology modifier, wherein the rheology modifier is selected from the group consisting of a (meth)acrylate polymer, a (meth)acrylate copolymer, and mixtures thereof; wherein the ink composition has a first dynamic viscosity of greater than about 1,100 cP at a shear rate of 0.1 sec⁻¹ measured at 25° C. and a second dynamic viscosity of less than about 100 cP at a shear rate of 1,000 sec⁻¹ measured at 25° C.

A cosmetic ink composition comprises: (a) a particulate material having a Particle Size Distribution D50 of from about 100 nm to about 2,000 nm; (b) a (meth)acrylic acid homopolymer or a salt thereof having a weight average molecular weight of less than about 20,000 daltons; and (c) from about 0.3 to about 1 active wt % of a rheology modifier, wherein the rheology modifier is selected from the group consisting of alkali swellable emulsion polymers, hydrophobically modified alkali swellable emulsion polymers, and combinations thereof; wherein the ink composition has a first dynamic viscosity of about 1,100 cP to about 10,000 cP at a shear rate of 0.1 sec⁻¹ measured at 25° C. and a second dynamic viscosity of from about 10 to about 100 cP at a shear rate of 1,000 sec⁻¹ measured at 25° C.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing out and distinctly claiming the present invention, it is believed the same will be better understood from the following description taken in conjunction with the accompanying drawings in which:

FIG. 1 is an exploded view of a personal care device for use in depositing the cosmetic ink composition described herein; and

FIG. 2 is an exploded view of a cartridge containing the cosmetic ink composition described herein.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, “active wt %” and “wt % (active)” refers to the amount of solid of an ingredient dissolved or suspended in water in the composition.

As used herein, “ambient conditions” refers to a temperature of about 23 degrees Celsius (° C.) and 50% relative humidity (RH).

As used herein, “Particle Size Distribution D50” refers to the diameter where fifty percent of the distribution has a smaller particle size.

As used herein, “Particle Size Distribution D90” refers to the diameter where ninety percent of the distribution has a smaller particle size.

As used herein, “separation” refers to the formation of a clear fluid layer at the top of a sample regardless of the uniformity of the particles in the sample below the clear fluid layer. Separation can include particle settling and/or syneresis.

As used herein, “settling” refers to the falling of particles in a composition due to gravity (according to Stokes' Law) to the bottom of a container. Particle settling can be affected by the size of the particles and their agglomeration over time.

As used herein, “static storage” refers to storage of a composition in the absence of vigorous or sustained vibration, agitation, or mixing prior to analysis or deposition of the composition.

As used herein, “syneresis” means phase separation, i.e. extraction or expulsion of a liquid from a gel, in this case a weak colloidal gel. The particles in a composition exhibiting syneresis are still uniformly suspended below the clear fluid layer.

As used herein, “ratio of (meth)acrylic acid homopolymer or a salt thereof to rheology modifier” refers to the ratio of the active wt % of the (meth)acrylic acid homopolymer or salt thereof divided by the active wt % of the rheology modifier.

As used herein, “the storage modulus” or “G′” refers to the measure of the stored energy, representing the elastic portion of the composition.

As used herein, “the loss modulus” or “G″” refers to the measure of the energy dissipated as heat, representing the viscous portion of the composition.

As used herein, “weight percent as added” refers to the amount of the total active plus water as added to the composition.

As used herein, “zeta potential” refers to the electrokinetic potential of the cosmetic ink composition.

As used herein, the articles “a” and “an” are understood to mean one or more of the material that is claimed or described, for example, “a rheology modifier” or “an active”.

All weights, measurements and concentrations herein are measured at ambient conditions unless otherwise specified.

All percentages, parts, and ratios as used herein are based upon the total weight of the cosmetic ink composition, unless otherwise specified. All such weights as they pertain to listed ingredients are based on the level as added in the composition, unless otherwise specified.

Cosmetic inks can require a white or light colored particulate material comprising particles large enough to be visually perceptible to the human eye in order to create opacity to cover skin imperfections. However, printing a cosmetic ink composition comprising a particulate material having a particle size large enough to be visually perceptible can be a challenge for current inks, printers, and/or cartridges. These challenges are caused primarily by the settling of the large, dense particles and secondarily by the packing of the settled particles in the cartridge. Re-mixing, either by automated mixing or hand shaking, may not be compatible with consumer in-home or hand-held printing purposes because of the vigorous and repeated re-mixing needed to keep the particles uniformly suspended.

Current opaque ink products can require repeated shaking, agitation, and/or rotation of the device and/or cartridge to keep the particles in a uniform suspension. This can be inconvenient to a consumer and is an additional step that consumers may not perform as instructed. If the particles are not re-dispersed, the cosmetic ink composition may not be uniform and/or the particles can become packed into the cartridge. Settling can be minimized by adding rheology modifiers to the ink. However, if the viscosity of the cosmetic ink composition is not well controlled, clogging and the speed of flow through the microfluidic channels and nozzles can make printing difficult. The use of dispersants in cosmetic ink compositions may help control agglomeration (i.e. the sticking of particles to one another) and hard packing of the particles; however, such formulations still require shaking to re-disperse the particles and do not exhibit particle suspension stability.

Described herein is a cosmetic ink composition that can exhibit long-term particle suspension stability and a personal care device for depositing the cosmetic ink composition. In one aspect, “stable white ink” can refer to an ink substantially free from particle settling, where no agitation or mixing is required to use the ink for its application.

In one aspect, the cosmetic ink composition described herein can be jetted onto any surface, preferably a keratinous surface including human skin and/or hair.

The cosmetic ink composition can comprise a unique combination of a rheology modifier and a (meth)acrylic acid homopolymer or a salt thereof that can suspend a particulate material having particles large enough to be visually perceptible, yet can still be jettable. Careful balancing of the agglomeration of the particles and viscosity of the cosmetic ink composition can be used to inhibit particle settling, providing particle suspension stability beyond which has been previously reported without hindering high frequency printing capabilities via thermal and/or piezo inkjet printheads. One advantage to this is that little to no shaking, and/or agitation of the cosmetic ink composition by the consumer or automated mechanical processes before and/or during printing is needed to re-disperse the particles. This can make the cosmetic ink composition more user-friendly as it does not require the consumer to perform an additional step to re-disperse the particles and/or can eliminate the need for agitation or rotation systems, including automated systems, within the printing device, cartridge, printer servicing station, and/or docking station.

Without being limited by theory, it is believed that the cosmetic ink composition can be stabilized using a (meth)acrylic acid homopolymer or a salt thereof to minimize and/or prevent particle agglomeration and a rheology modifier to introduce a secondary structure and build viscosity to suspend the particles in a weak colloidal gel. The colloidal gel can be strong enough to hold the particles in suspension when not printing (thus inhibiting particle settling), but weak enough to break up during printing.

In particular, it was found that a cosmetic ink composition comprising a particulate material, such as TiO₂, a rheology modifier selected from the group consisting of alkali swellable emulsion (“ASE”) polymers, hydrophobically modified alkali swellable emulsion (“HASE”) polymers, and combinations thereof, and a (meth)acrylic acid homopolymer or a salt thereof can be stable, yet still jettable using standard cartridges and nozzles in a thermal and/or piezo printer.

It was found that the cosmetic ink composition described herein can have a first dynamic viscosity at a shear rate of 0.1 sec⁻¹ measured at 25° C. of greater than about 1,100 cP, which can prevent settling of the particles. It was further found that the cosmetic ink composition can have a second dynamic viscosity at a shear rate of 1,000 sec⁻¹ measured at 25° C. of less than about 100 cP, which can prevent clogging and speed of flow issues through the cartridge and/or nozzles. Without being limited by theory, it is believed that a shear rate of 0.1 sec⁻¹ can be representative of storage conditions, while a shear rate of 1,000 sec⁻¹ can be representative of printing conditions.

In one aspect, the cosmetic ink composition need not be agitated or shaken to re-disperse the particles before and/or during use because the particles can remain in suspension over the shelf-life of the product.

Cosmetic Ink Composition

In one aspect, the cosmetic ink composition can be a skin care composition. The cosmetic ink composition can hide or camouflage a skin imperfection, such as hyperpigmentation, when deposited precisely and substantially only onto the skin imperfection.

The cosmetic ink composition can be non-Newtonian, meaning the cosmetic ink composition can have a shear dependent viscosity and/or viscoelastic properties. The cosmetic ink composition can show shear thinning effects under the fluid ejection conditions in which the ink is moved between the cartridge and the printhead of an inkjet device. When the cosmetic ink composition is jetted, the shear rate can increase, resulting in a decrease in the viscosity. Thus, the cosmetic ink composition can be stored without particle settling, yet the viscosity and particle size are such that the cosmetic ink composition can still be printed.

The cosmetic ink composition can comprise a particulate material, a (meth)acrylic acid homopolymer or a salt thereof, and a rheology modifier.

In one aspect, the particulate material can be hydrophilic. In one aspect, the particulate material can be substantially coated with one or more ingredients to cause the particulate material to become more hydrophilic. As used herein, “substantially coated” can mean at least about 25%, preferably greater than about 50% surface coverage of the particulate material, more preferably greater than about 75%, most preferably greater than about 90%. Suitable coating ingredients that can render the particulate material hydrophilic in nature can include silica, alumina, polyethylene glycol (PEG) 12 dimethicone, phytic acid, sodium glycerophosphate, and combinations thereof. The particulate material can be substantially coated with one or more coating ingredients using techniques known in the art. One advantage to using a hydrophilic particulate material is that hydrophilic particulate material can be more easily dispersed in water. In one aspect, the particulate material can be titanium and/or iron oxide which has been substantially coated with silica and/or alumina.

Suitable particulate materials can include pigments; encapsulated pigments; mica; clay; mixed metal oxide pigments; metal oxides such as iron oxide, titanium dioxide, zinc oxide, aluminum hydroxide, iron oxide, and combinations thereof; boron nitride; silica; talc; basic lead carbonate; magnesium silicate; baryte (BaSO₄); calcium carbonate; pearlescent; colorants, including natural colorants and synthetic monomeric and polymeric colorants; dyes such as azo, indigoid, triphenylmethane, anthraquinone, and xanthine dyes which are designated as D&C and FD&C blues, browns, greens, oranges, reds, yellows, etc.; insoluble metallic salts of certified color additives, referred to as the Lakes; and combinations thereof.

In one aspect, the particulate material can comprise titanium dioxide, iron oxide, and combinations thereof. In one aspect, the titanium dioxide and/or iron oxide can be readily dispersed in water. In one aspect, the titanium dioxide and/or iron oxide is not hydrophobically treated before use in the cosmetic ink composition because it may not be readily dispersed in water. Suitable particulate material can include slurries of titanium dioxide and iron oxide available from KOBO Products Inc (South Plainfield, N.J.), or equivalents.

In one aspect, the cosmetic ink composition comprises a white pigment.

In one aspect, the cosmetic ink composition can have a white appearance. Alternatively, the cosmetic ink composition can have a white appearance with tints of red and/or yellow.

Typical levels of particulate material for sufficient opacity to hide and/or camouflage skin imperfections can be around 30 active wt %. In one aspect, the cosmetic ink composition can comprise greater than about 15 active wt % particulate material, alternatively greater than about 20 active wt %, alternatively greater than about 30 active wt %. In one aspect, the cosmetic ink composition can comprise from about 1 to about 30 active wt % particulate material, alternatively from about 3 to about 25 active wt %, alternatively from about 5 to about 20 active wt %, alternatively from about 8 to about 18 active wt %.

The particulate material can comprise particles having a Particle Size Distribution (PSD) D50 of about 100 nm to about 2,000 nm, alternatively from about 150 nm to about 1,000 nm, alternatively from about 200 nm to about 450 nm, alternatively from about 200 nm to about 350 nm. In one aspect, the particulate material can comprise particles having a PSD D90 of less than about 2 μm, alternatively less than about 1 μm. In one aspect, the particulate material can comprise particles having a PSD D90 of from about 700 to about 900 μm. Without being limited by theory, it is believed that if the particles are too big, they can clog the microfluidic channels of the cartridge and disrupt printing. One skilled in the art would understand that an acceptable particle size can vary depending on printhead die architecture. In one aspect, the particulate material can comprise any PSD so long as the particles can move through the microfluidic channels of the cartridge and/or the printhead without causing clogging. The Particle Size Distribution can be measured according to the Particle Size Distribution Method described hereafter.

The particulate material can have a refractive index of between about 1.1 and about 5.0, alternatively from about 1.5 to about 4, alternatively from about 2 to about 3.

The particulate material can have a density range of from about 1.5 to about 6 g/mL, alternatively from about 2 to about 4 g/mL.

The cosmetic ink composition can comprise a rheology modifier. Rheology modifiers can assist in preventing settling by keeping the particles uniformly suspended such that little to no agitation of the cosmetic ink composition is needed.

One preferred group of rheology modifiers are ASE polymers. ASE polymers contain a balance of hydrophilic (meth)acrylic acid monomers and hydrophobic (meth)acrylate ester monomers and can be supplied at high volume solids in liquid form. ASE polymers rely on a change from low to high pH (neutralization) to trigger thickening. The “trigger” is built into the polymer by creating an approximately 50:50 ratio of (meth)acrylic acid, which is soluble in water, and a (meth)acrylate ester, which is not soluble in water. When the acid is un-neutralized (low pH), the polymer is insoluble in water and does not thicken. When the acid is fully neutralized (high pH), the polymer becomes soluble and thickens. ASE polymers are supplied at low pH (<5) and maintain a low as-supplied viscosity (<100 cP) at solids of up to 35%. When subject to a pH of about 7 or higher, ASE polymers solubilize, swell, and thicken the composition through volume exclusion. The degree of thickening can be related to the molecular weight of the polymer. Because their performance depends on water absorption and swelling, ASE polymers tend to be very high in molecular weight, which allows them to thicken efficiently. The rheology profiles ASE polymers create are typically steeply shear-thinning (pseudoplastic), and thus ASE polymers are well suited to build high viscosity at very low shear rates. Different rheological characteristics can be achieved by manipulating the molecular weight, as well as the types and amounts of acid and ester monomers, of the polymer.

In one aspect, the hydrophilic monomers of the ASE polymer can include (meth)acrylic acid and maleic acid. In one aspect, the hydrophobic monomers of the ASE polymer can include the esters of (meth)acrylic acid with C₁- to C₄-alcohols, in particular ethyl acrylate, butyl acrylate, and methyl methacrylate.

In one aspect, the ASE polymer can be synthesized from 10-90 wt % of Hydrophilic Monomer A and 10-90 wt % of Hydrophobic Monomer B. The structure of Hydrophilic Monomer A and Hydrophobic Monomer B are shown below.

wherein R₁ and R₂ are independently hydrogen or methyl; wherein R₃ is C₁ to C₄ alkyl.

Yet another group of rheology modifier suitable for use in the cosmetic ink composition described herein are HASE polymers. These are tertiary polymers that build on the ASE polymer chemistry by adding a hydrophobic acrylic ester and/or vinyl ester monomer to the polymer composition. HASE polymers retain the pH dependent behavior of their ASE counterparts, but in addition to absorbing water, HASE polymers also thicken via hydrophobe association. This mechanism, known as associative thickening (i.e. associating with any hydrophobic moiety in the composition), offers performance properties over a wider range of shear levels and enables a wider range of rheology profiles than is possible with volume exclusion thickeners such as ASE and cellulosic compositions.

The hydrophilic and hydrophobic monomers of the HASE polymers can be the same as described with respect to the ASE polymers. The associative monomer of the HASE polymer can be a monomer that shows a strong hydrophobic character. A preferred associative monomer is ester of (meth)acrylic acid with C₈-C₂₂ alcohols.

In one aspect, the HASE polymer can be synthesized from 10-90 wt % Hydrophilic Monomer A, 10-90 wt % Hydrophobic Monomer B, and 0.01 to 2 wt % Associative Monomer C. The structure of Associate Monomer C is shown below.

wherein R₄ is hydrogen or methyl; wherein R₅ is C₈ to C₂₂ alkyl; wherein n is an integer from 0 to 50.

Alternatively, the HASE polymer can be synthesized from 10-90 wt % Hydrophilic Monomer A, 10-90 wt % Hydrophobic Monomer B, and 0.01 to 2 wt % Associative Monomer D. The structure of Associative Monomer D is shown below.

wherein R₆ is hydrogen or methyl; wherein R₇ is C₈ to C₂₂ alkyl.

In one aspect, the associative monomer can be selected from the group consisting of steareth-20 methacrylate, beheneth-25 methacrylate, vinyl neodecanoate, and combinations thereof. In one aspect, more than one associative monomers can be used in the synthesis of the HASE polymer.

In one aspect, ASE and HASE polymers can comprise a cross-linking agent. The cross-linking agent can contain at least two ethylenically unsaturated moieties, alternatively at least three ethylenically unsaturated moieties. Suitable cross-linking agents can include divinyl benzene, tetra allyl ammonium chloride, allyl acrylates, methacrylates, diacrylates, dimethacrylates of glycols and polyglycols, butadiene, 1,7-octadiene, allyl-acrylamides, allyl-methacrylamides, bisacrylamidoacetic acid, N, N′-methylene-bisacrylamide, polyol polyallylethers such as polyallylsaccharose and pentaerythrol triallylether, and mixtures thereof.

In one aspect, the cross-linking agent can be present at a level of from about 25 to about 5,000 ppm, alternatively from about 50 to about 1,000 ppm, alternatively from about 100 to about 500 ppm.

Another group of rheology modifiers are hydrophobically-modified ethylene oxide-based urethane (HEUR) polymers. Unlike ASE or HASE-type rheology modifiers, HEUR polymers are non-ionic and soluble at any pH. This solubility is due to the polymer's ethylene oxide backbone, which is water soluble and makes up the majority of the polymer structure. Thus, HEUR polymers require a hydrophobic moiety in the composition to interact with the ethylene oxide backbone to impart structure. The cosmetic ink composition can comprise a HEUR polymer. Alternatively, the cosmetic ink composition comprises little to no hydrophobic moieties and does not comprise a HEUR polymer.

The rheology modifier can be a (meth)acrylate polymer, a (meth)acrylate copolymer, and mixtures thereof. The rheology modifier can be selected from the group consisting of ASE polymers, HASE polymers, and combinations thereof. Suitable HASE polymers can include ACULYN™ Excel; ACRYSOL™ TT615; ACULYN™ 22; ACULYN™ 88; (all available from The DOW Chemical Company, Lake Zurich, Ill.); and combinations thereof. Suitable ASE polymers can include Rheovis® 1125 (available from BASF Corporation, Charlotte, N.C.), ACULYN™ 33; ACULYN™ 38 (both available from The DOW Chemical Company, Lake Zurich, Ill.); and combinations thereof. The cosmetic ink composition can comprise an ASE polymer. Alternatively, the cosmetic ink composition can comprise an HASE polymer.

The rheology modifier does not consist of a surfactant, an amine oxide, and/or a cellulosic ether.

The cosmetic ink composition can comprise any amount of rheology modifier so long as the first dynamic viscosity of the cosmetic ink composition is greater than about 1,100 cP at a shear rate of 0.1 sec⁻¹ measured at 25° C. The cosmetic ink composition can comprise greater than about 0.30 active wt % rheology modifier, alternatively greater than about 0.40 active wt %, alternatively greater than about 0.50 active wt %. The cosmetic ink composition can comprise from about 0.30 to about 1 active wt % rheology modifier, alternatively from about 0.30 to about 0.80 active wt %, alternatively from about 0.40 to about 0.50 active wt %. Active wt % can be measured using standard High Performance Liquid Chromatography-Mass Spectrometry (HPLC-MS) techniques. One advantage to keeping the level of rheology modifier within this range is that the viscosity of the cosmetic ink composition can be built such that the particles can be suspended in the composition. The particles can be suspended for about 11 days or more at 25° C., alternatively about 30 days or more at 25° C., alternatively for about 90 days or more at 25° C., alternatively for about 300 days or more at 25° C. Without being limited by theory, it is believed that at levels of rheology modifier below this range the particles may not be sufficiently suspended and settling may occur. If the level of rheology modifier is too high, the viscosity of the cosmetic ink composition may increase to a point that can impact jetting (i.e. the cosmetic ink composition may not shear thin enough for efficient printing).

In one aspect, the cosmetic ink composition can be substantially free of neutral inorganic salts (as compared to an alkali salt base, like NaOH). Without being limited by theory, it is believed that neutral inorganic salts, such as calcium chloride or sodium chloride, can increase the ionic strength of the cosmetic ink composition and can disrupt the internal structure, thus impacting stability. It is known that HASE and/or ASE polymers become polyelectrolytes at high pHs. As pH increases, the carboxylic acids on the HASE and/or ASE polymers can be neutralized, generating ionic groups on the polymer chains that can produce electrostatic repulsion. These electrostatic repulsions can cause the polymer to expand and form an internal structure in the composition. It is believed that inorganic neutral salts can shield this electrostatic repulsion and can cause the HASE and/or ASE polymer to change structure, and thus its effectiveness in promoting stability.

The cosmetic ink composition can comprise a (meth)acrylic acid homopolymer or a salt thereof. Non-limiting examples of acceptable salts can include sodium, potassium, ammonium, and mixtures thereof. The (meth)acrylic acid homopolymer or salt thereof can be a low molecular weight material that can act to control particle size and can help maintain a low viscosity in the cosmetic ink composition. The (meth)acrylic acid homopolymer or salt thereof does not greatly increase viscosity of the cosmetic ink composition. Non-limiting examples of suitable (meth)acrylic acid homopolymers or salt thereof can include sodium polyacrylate such as Darvan® 811D (available from RT Vanderbilt Holding Company Inc., Norwalk, Conn.), ammonium polyacrylate having a weight average molecular weight of about 3,500 daltons such as Darvan® 821A (available from RT Vanderbilt Holding Company Inc.), and combinations thereof. The (meth)acrylic acid homopolymer or salt thereof have a weight average molecular weight of less than about 20,000 daltons, preferably less than about 10,000 daltons, more preferably less than about 5,000 daltons. The cosmetic ink composition can comprise a (meth)acrylic acid homopolymer or salt thereof having a weight average molecular weight of from about 1,000 to about 20,000 daltons, alternatively from about 1,000 to about 10,000 daltons, alternatively from about 2,000 to about 5,000 daltons, alternatively from about 2,500 to about 4,000 daltons. Weight average molecular weight can be measured by standard High Performance Size-Exclusion Chromatography per ASTM method D5296-11 (Sep. 1, 2011).

In one aspect, the (meth)acrylic acid homopolymer or salt thereof is not a film forming polymer. Without being limited by theory it is believed that the (meth)acrylic acid homopolymer or salt thereof will not form a film because of the low molecular weight.

The cosmetic ink composition can comprise from about 0.01 to about 1 active wt % (meth)acrylic acid homopolymer or salt thereof, alternatively from about 0.10 to about 0.85 active wt %, alternatively from about 0.20 to about 0.75 active wt %, alternatively about 0.30 to about 0.65 active wt %. Without being limited by theory, it is believed that the (meth)acrylic acid homopolymer or salt thereof can control agglomeration, and thus the particle size, of the particulate material by creating a negative surface charge around the particles. Thus, the (meth)acrylic acid homopolymer or salt thereof can help to maintain a particle size that is compatible with printer cartridges and nozzles. Without being limited by theory, it is believed that a cosmetic ink composition comprising below 0.01 active wt % (meth)acrylic acid homopolymer or salt thereof may not have sufficient particle size control and/or the viscoelastic modulus may be too high to allow for reliable refill of the microfluidics.

The ratio of the (meth)acrylic acid homopolymer or salt thereof to the rheology modifier can be less than about 1. The ratio of (meth)acrylic acid homopolymer or salt thereof to rheology modifier can be from about 0.10 to about 0.75, alternatively from about 0.30 to about 0.65. Without being limited by theory it is believed that if the level of (meth)acrylic acid homopolymer or salt thereof is greater than the level of rheology modifier, the rheology modifier may not be able to build the internal structure needed to suspend the particles. If the ratio of (meth)acrylic acid homopolymer or salt thereof to rheology modifier is too low, agglomeration may not be well controlled and the particle size may become too large to fit through printer nozzles, making printing difficult.

It is believed that stability is inversely proportional to the level of (meth)acrylic acid homopolymer or salt thereof and directly proportional to the level of rheology modifier.

The cosmetic ink composition can have a first dynamic viscosity of greater than about 1,100 cP at a shear rate of 0.1 sec⁻¹ measured at 25° C. and a second dynamic viscosity of less than about 100 cP at a shear rate of 1,000 sec⁻¹ measured at 25° C. The cosmetic ink composition can have a first dynamic viscosity of from about 1,100 cP to about 10,000 cP at a shear rate of 0.1 sec⁻¹ at 25° C., alternatively from about 1,500 cP to about 8,000 cP, alternatively from about 2,000 cP to about 5,000 cP. The cosmetic ink composition can have a second dynamic viscosity of from about 10 cP to about 100 cP at a shear rate of 1,000 sec⁻¹ at 25° C., alternatively from about 20 to about 80 cP. Viscosity can be measured according to the Viscosity Test Method described hereinafter. One advantage to having a first and second dynamic viscosity in this range is that at high shear rate, the cosmetic ink composition can drop to a viscosity that is similar to Newtonian inks, yet can still maintain a viscosity sufficient to suspend the particles when not printing.

The cosmetic ink composition can have a first dynamic viscosity measured at a shear rate of 0.1 sec⁻¹ at 25° C. that is about 70% higher than the second dynamic viscosity of the cosmetic ink composition when measured at a shear rate of 1,000 sec⁻¹ at 25° C., alternatively about 80% higher, alternatively about 90% higher, alternatively about 95% higher. The cosmetic ink composition can have a first dynamic viscosity measured at a shear rate of 0.1 sec⁻¹ at 25° C. that is about 25 times greater than the second dynamic viscosity of the cosmetic ink composition when measured at a shear rate of 1,000 sec⁻¹ at 25° C., alternatively about 35 times greater, alternatively about 50 times greater, alternatively about 80 times greater.

The cosmetic ink composition can have temperature dependent viscosity. Lower viscosity was observed at a shear rate of 1000 sec⁻¹ at an elevated temperature of about 70° C.

The cosmetic ink composition can have a storage modulus (G′) of from about 2 to about 10, alternatively from about 3 to about 8, alternatively from about 4 to about 6. Without being limited by theory, it is believed that if the G′ of the cosmetic ink composition is greater than about 10, the decap or start up after idle time in the printhead may be difficult without intervention because the composition is too elastic. Storage modulus can be measured according to the Oscillatory Strain Sweep Method described hereafter.

The cosmetic ink composition can have a loss modulus (G″) of from about 1 to about 5, alternatively from about 1.5 to about 4, alternatively from about 2 to about 3. Loss modulus can be measured according to the Oscillatory Strain Sweep Method described hereafter.

The ratio of loss modulus to storage modulus, or tan(delta), is a useful representation of the extent of elasticity in a fluid. In this case, it can be a measure of the intrinsic stability of the cosmetic ink composition. When G″ is higher than G′, tan(delta) is greater than about 1 and indicates a viscous dominant fluid behavior. When G′ is higher than G″, tan(delta) is less than about 1 and indicates an elastic dominant fluid behavior.

The cosmetic ink composition can have a tan(delta) of about 1. Alternatively, the cosmetic ink composition can have a tan(delta) of less than about 1, alternatively less than about 0.6. Without being limited by theory it is believed that when the tan(delta) is less than about 0.6, particle settling can be minimized and/or prevented. The cosmetic ink composition can have a tan(delta) of from about 0.2 to about 1, alternatively from about 0.4 to about 0.9, alternatively from about 0.6 to about 0.8.

The cosmetic ink composition can have a zeta potential of about negative 20 or less, alternatively about negative 30 or less, alternatively greater than about positive 20, alternatively greater than about positive 30. The cosmetic ink composition can have a zeta potential of about negative 20 or less, or greater than about positive 20. One advantage to having a zeta potential in this range is that the surface charge of the particles can be increased, thus preventing agglomeration of the particles. Zeta potential can be measured according to the Zeta Potential Test Method described hereafter.

The cosmetic ink composition can have a neat pH of greater than about 7.5. The cosmetic ink composition can have a neat pH of about 7.5 to about 9.0, alternatively from about 7.5 to about 8.5. Without being limited by theory, it is believed that at a pH lower than about 7.5, syneresis can occur at a faster rate. It is believed that at a lower pH, the equilibrium between the carboxylic acid and carboxylate salts of the rheology modifier can be pushed toward the protonated acid and therefore are not available to suspend the particles. It is believed that as the pH increases, the larger the negative zeta potential becomes, thus preventing agglomeration of the particles. The cosmetic ink composition can comprise a buffering agent for adjusting the pH conditions. The buffering agent can be any basic excipient. In one aspect, the buffering agent can be a strong base, such as sodium hydroxide, potassium hydroxide, calcium hydroxide, and mixtures thereof. The neat pH of the cosmetic ink composition can be measured by standard methodology known to those skilled in the art.

The cosmetic ink composition can have a surface tension of from about 25 to about 60 dyn/cm, alternatively from about 30 to about 55 dyn/cm, alternatively from about 40 to about 50 dyn/cm.

The cosmetic ink composition can have an opacity of at least 0.2. In one aspect, the cosmetic ink composition can comprise an opacity of from about 0.2 to about 1, alternatively from about 0.25 to about 0.8, alternatively from about 0.3 to about 0.5.

The cosmetic ink composition can be substantially free of particle settling. Substantially free of particle settling can mean that the variation between the weight % solids of the top and bottom of a sample of the cosmetic ink composition is less than 5% at ambient conditions at 4 days after formulation, alternatively less than about 3%, alternatively less than about 1%. Particle settling can be measured according to the Particle Settling Test Method described hereafter.

The cosmetic ink composition can be substantially free of particle agglomeration. Substantially free of particle agglomeration can mean that the cosmetic ink composition exhibits less than about 25 nm of particle growth per month at ambient conditions, alternatively less than about 15 nm, alternatively less than about 10 nm. The rate of agglomeration can be determined by measuring particle size according to the Particle Size Distribution method described hereafter over a period of time.

The cosmetic ink composition can have less than about 10% separation at 11 days after formulation at 25° C., alternatively less than about 5%, alternatively less than about 2%, alternatively less than about 1%. In one aspect, the cosmetic ink composition can have less than about 4 mm of separation at 11 days after formulation at 25° C., alternatively less than about 2 mm, alternatively less than about 1 mm, alternatively less than about 0.50 mm. Separation can be measured according to the Separation Test Method described hereafter.

The cosmetic ink composition can have a shelf-life of about 1 month, alternatively about 3 months, alternatively about 6 months, alternatively about 12 months, alternatively about 18 months, alternatively about 24 months. As used herein, “shelf-life” means the amount of time the particles can remain uniformly suspended in the cosmetic ink composition at ambient conditions without the need for shaking or agitation.

The cosmetic ink compositions may further comprise a humectant as a carrier or chassis for the other components in the cosmetic ink composition. An exemplary class of humectants can include polyhydric alcohols. Suitable polyhydric alcohols can include polyalkylene glycols and alkylene polyols and their derivatives, including propylene glycol, dipropylene glycol, polypropylene glycol, polyethylene glycol and derivatives thereof; sorbitol; hydroxypropyl sorbitol; erythritol; threitol; pentaerythritol; xylitol; glucitol; mannitol; butylene glycol (e.g., 1,3-butylene glycol); pentylene glycol; hexane triol (e.g., 1,2,6-hexanetriol); glycerin; ethoxylated glycerine; propoxylated glycerine; and mixtures thereof.

Other suitable humectants can include sodium 2-pyrrolidone-5-carboxylate; guanidine; glycolic acid and glycolate salts (e.g., ammonium and quaternary alkyl ammonium); lactic acid and lactate salts (e.g., ammonium and quaternary alkyl ammonium); aloe vera in any of its variety of forms (e.g., aloe vera gel); hyaluronic acid and derivatives thereof (e.g., salt derivatives such as sodium hyaluronate); lactamide monoethanolamine; acetamide monoethanolamine; urea; sodium pyroglutamate, water-soluble glyceryl poly(meth)acrylate lubricants (such as Hispagel®, available from BASF, Ludwigshafen, Germany); and mixtures thereof.

The cosmetic ink composition can comprise from about 1 to about 40 active wt % humectant, alternatively from about 5% to about 35%, alternatively from about 10% to about 30%, alternatively from about 15% to about 20%. Alternatively, the cosmetic ink composition can comprise from about 20 to about 30 active wt % humectant.

Without being limited by theory, it is believed that at a level of about 20 active wt % or more the humectant can help prevent drying and/or clogging of the nozzles and/or cartridge when the cosmetic ink composition is not being printed.

In one aspect, the level of humectant is less than about 30 active wt % to promote fast dry times of the cosmetic ink composition on the skin.

The cosmetic ink composition can be delivered alone or in the presence of a dermatologically-acceptable carrier. The phrase “dermatologically-acceptable carrier”, as used herein, means that the carrier is suitable for topical application to a keratinous tissue, has good aesthetic properties, is compatible with any additional components of the cosmetic ink composition, and/or will not cause any untoward safety or toxicity concerns. In one aspect, the cosmetic ink composition is safe for use on skin. In one aspect, the cosmetic ink composition does not comprise alkyds, celluloses, formaldehydes, phenolics, ketones, rubber resins, and combinations thereof because such ingredients may not be compatible with use on human skin. In one aspect, the cosmetic ink composition can be hypoallergenic. Water is by far the most common carrier, and is typically used in combination with other carriers. The carrier can be in a wide variety of forms. Non-limiting examples include simple solutions (water or oil based) or emulsions. The dermatologically acceptable carrier can be in the form of an emulsion. Emulsion may be generally classified as having a continuous aqueous phase (e.g., oil-in-water and water-in-oil-in-water) or a continuous oil phase (e.g., water-in-oil and oil-in-water-in-oil). The oil phase may comprise silicone oils, non-silicone oils such as hydrocarbon oils, esters, ethers, and the like, and mixtures thereof. For example, emulsion carriers can include, but are not limited to, continuous water phase emulsions such as silicone-in-water, oil-in-water, and water-in-oil-in-water emulsion and continuous oil phase emulsions such as water-in-oil and water-in-silicone emulsions, and oil-in-water-in-silicone emulsions.

The cosmetic ink composition can comprise water, preferably deionized water. The cosmetic ink composition can comprise from about 40% to about 75% water, by weight of the cosmetic ink composition, alternatively from about 55% to about 70%, alternatively from about 60% to about 68%.

Additionally, the cosmetic ink composition can optionally include anti-fungal and/or anti-bacterial components. Examples of anti-fungal and/or anti-bacterial components can include isothiazolinone such as methylisothiazolinone and methylchloroisothiazolinone.

The cosmetic ink composition can optionally comprise a preservative. Non-limiting examples of suitable preservatives can include phenoxy ethanol, 1,2-Hexanediol, 1,2-Octanediol (commercially available as SymDiol® 68 from Symrise, AG, Branchburg, N.J.), farnesol, 2-methyl 5-cyclohexypentanol, 1,2-decanediol, and combinations thereof. The cosmetic ink composition can comprise from about 0.01% to about 10% preservative, alternatively from about 0.1% to about 5%, alternatively from about 1% to about 3%, all by weight of the cosmetic ink composition. One advantage to including a preservative is that it can help to prevent microbial growth in the cosmetic ink composition, for instance if the cosmetic ink composition becomes contaminated with bacteria from the skin.

The cosmetic ink composition may comprise a monohydric alcohol. The cosmetic ink composition can comprise about 50 ppm or more of a monohydric alcohol. The cosmetic ink composition can comprise from about 50 to about 10,000 ppm of a monohydric alcohol, alternatively from about 100 to about 5,000 ppm, alternatively from about 100 to about 1,000 ppm. Suitable monohydric alcohols include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol and 2-methyl-2-propanol.

The cosmetic ink composition may comprise a safe and effective amount of one or more skin care actives (“active”) useful for regulating and/or improving the skin. “Safe and effective amount” means an amount of a compound or composition sufficient to induce a positive benefit but low enough to avoid serious side effects (i.e., provides a reasonable benefit to risk ratio within the judgment of a skilled artisan). A safe and effective amount of an active can be from about 1×10⁻⁶ to about 25%, alternatively from about 0.0001 to about 20%, alternatively from about 0.01 to about 10%, alternatively from about 0.1 to about 5%, alternatively from about 0.2 to about 2%, all by weight of the cosmetic ink composition.

Suitable skin care actives include, but are not limited to, vitamins (e.g., B3 compounds such as niacinamide, niacinnicotinic acid, and tocopheryl nicotinate; B5 compounds such as panthenol; vitamin A compounds and natural and/or synthetic analogs of Vitamin A, including retinoids, retinol, retinyl acetate, retinyl palmitate, retinoic acid, retinaldehyde, retinyl propionate, and carotenoids (pro-vitamin A); vitamin E compounds, or tocopherol, including tocopherol sorbate and tocopherol acetate; vitamin C compounds, including ascorbate, ascorbyl esters of fatty acids, and ascorbic acid derivatives such as magnesium ascorbyl phosphate and sodium ascorbyl phosphate; ascorbyl glucoside; and ascorbyl sorbate); peptides (e.g., peptides containing ten or fewer amino acids, their derivatives, isomers, and complexes with other species such as metal ions); sugar amines (e.g., N-acetyl-glucosamine); sunscreens; oil control agents; tanning actives; anti-acne actives; desquamation actives; anti-cellulite actives; chelating agents; skin lightening agents; flavonoids; protease inhibitors (e.g., hexamidine and derivatives); non-vitamin antioxidants and radical scavengers; salicylic acid; hair growth regulators; anti-wrinkle actives; anti-atrophy actives; minerals; phytosterols and/or plant hormones; tyrosinase inhibitors; N-acyl amino acid compounds; inositol; undecylenoyl phenylalanine; moisturizers; plant extracts; and derivatives of any of the aforementioned actives; and combinations thereof. The term “derivative” as used herein refers to structures which are not shown but which one skilled in the art would understand are variations of the basic compound. For example, removing a hydrogen atom from benzene and replacing it with a methyl group.

In one aspect, the cosmetic ink composition can comprise peroxide, including hydrogen peroxide and/or benzoyl peroxide.

In one aspect, the cosmetic ink composition can comprise a skin care active selected from the group consisting of niacinamide; inositol; undecylenoyl phenylalanine; and combinations thereof.

In one aspect, the cosmetic ink composition is substantially free of latex polymer binders and/or a film forming polymers. In one aspect, the cosmetic ink composition comprises less than about 10% latex polymer binders and/or film forming polymers, alternatively less than about 1%, alternatively less than about 0.1%. Without being limited by theory, it is believed that latex polymer binders and/or film forming polymers can make printing can be difficult because these polymers can solidify after evaporation and irreversibly plug the nozzles.

In one aspect, the cosmetic ink composition comprises from about 10% to about 30% solids. In one aspect, the cosmetic ink composition comprises less than 40% solids. Without being limited by theory, it is believed that at a solids level of greater than 40%, such as in prepaints or paints, printing can be difficult because a high level of solids may lead to irreversible nozzle clogging.

In one aspect, the cosmetic ink composition can be removeable with water, alternatively with soap and water.

Personal Care Device

In one aspect, the cosmetic ink composition described herein can be applied to the skin using a hand-held personal care device. The personal care device can analyze the skin, identify skin imperfections, and deposit the cosmetic ink composition onto the identified skin imperfection in order to hide and/or camouflage the skin imperfection. An exemplary personal care device is described in U.S. Pat. No. 9,522,101.

In one aspect, the personal care device can comprise a sensor configured to take at least one image of skin and a processor configured to calculate the average background lightness value of the image on a grey scale (lightness value on a grey scale is herein referred to as “L value”). Further, from the same image, a local L value can be calculated for individual pixels or a group of pixels. The processor can then compare the local L value to the background L value to identify skin imperfections. When a skin imperfection is identified, the processor can activate one or more nozzles to fire and dispense the cosmetic ink composition onto the skin imperfection.

A skin imperfection is an area of skin where the absolute value of the difference between a local L value and the background L, this difference being defined as the measured delta L (“ΔL_(M)”), is greater than a predetermined set delta L (“ΔL_(S)”). The background L can be preset or calculated anywhere within the image. The image can be taken where the nozzles will fire the cosmetic ink composition. The background L can be the arithmetic average, median, or mean of a plurality of local Ls, which means the calculation can include all of the local Ls in the image, or a subset thereof.

FIG. 1, shows an exploded view of personal care device 40. Physical spacer 42 of personal care device 40 is directly above skin surface 18. Physical spacer 42 has a set, predetermined height a such that when it contacts skin surface 18, the mechanical and electrical elements are all at a known distance from skin surface 18. In one aspect, the height a is from about 1 mm to about 20 mm, alternatively from about 3 mm to about 15 mm, alternatively from about 4 mm to about 10 mm.

The mechanical and electrical elements associated with personal care device 40 can include, but are not be limited to, light 44, sensor 46, nozzle array 20 which is embedded on cartridge die 57 which is attached to cartridge 52. Cartridge die 57 can be made of silicon, glass, machinable glass ceramic, sapphire, alumina, printed wiring board substrates (for example, Liquid Crystal Polymer, polyimide etc.) within which nozzle array 20 can be formed. Nozzle array 20 can be in a linear configuration, multiple rows, off-set, sine wave, curved, circular, saw tooth arrangements, and combinations thereof. All of these elements can be enclosed within optional apparatus housing 41.

Light 44 can illuminate the area of skin surface 18 within physical spacer 42 such that sensor 46 has relatively constant illumination. Background lighting can affect sensor 46 as portions of physical spacer 42 lift off skin surface 18 and allow background light in and the illumination from light 44 to escape. Small deviations in illumination can be corrected for provided light 44 provides a relatively constant background illumination. In one aspect, physical spacer 42 can be opaque. Light 44 can be a LED, incandescent light, neon bulb based, or any other commercially available source of illumination. Light 44 can have constant illumination or adjustable illumination. For example, an adjustable light source might be useful if the background illumination is excessively bright or dark.

Sensor 46 can be any component that is capable of obtaining a visual property of an area of skin surface. Non-limiting examples of sensors can include optical sensors, image capture devices, spectrophotometers, photonic measuring devices for wavelengths within the visible spectrum as well as those wavelengths above and below the visible spectrum which could measure sub-surface features, and combinations thereof. The image capture device can be any of a variety of commercially available devices such as a simple camera or a digital cmos camera chip. In one aspect, the image capture device can be a camera and the images can be taken or converted to a standard grey scale that is known in the art. It is understood that any numerical scale that measures lightness to darkness can be considered a “grey scale”. Moreover, as used herein, “grey scale” is intended to be a linear scale, or one band, or one visual attribute. For example, one “grey scale” visual attribute could be single wavelength or a narrow wavelength to define a specific visual color. Another example of one “grey scale” visual attribute could be a mix of wavelength numerical values averaged for each pixel making up the image, such as a true black, grey or white image from an RGB mixture.

Sensor 46 can take a measurement of the L value of skin surface 18 and/or an image of skin surface 18 and can send it to processor 50 via image capture line 48 for analysis. The image may be analyzed for local L values, background L values, or both. Grey scale conversion can occur within the analytical processing capabilities of processor 50. The comparison of background L to local L to determine the ΔL_(M) occurs within processor 50, which can be a commercially available programmable chip, or other commercially available processing units.

Processor 50 is generally referred to as a central processing unit (“CPU”). The CPU can be a single programmable chip like those found in consumer electronic devices such as a laptop computer, a cell phone, an electric razor, and the like. The CPU may comprise an Application Specific Integrated Circuit (ASIC), controller, Field Programmable Gate Array (FPGA), integrated circuit, microcontroller, microprocessor, processor, and the like. The CPU may also comprise memory functionality, either internal to the CPU as cache memory, for example Random Access Memory (RAM), Static Random Access Memory (SRAM), and the like, or external to the CPU, for example as Dynamic Random-Access Memory (DRAM), Read Only Memory (ROM), Static RAM, Flash Memory (e.g., Compact Flash or SmartMedia cards), disk drives, Solid State Disk Drives (SSD), or Internet Cloud storage. While it is anticipated that a remote CPU, either tethered to the personal care device or which communicates wirelessly, can be used, a local CPU within the personal care device is exemplified herein.

Images can be taken in sequence or preferably continuously. The image capture device can take images at a speed of at least 4 frames per second, alternatively at least 100 frames per second, alternatively at least 200 frames per second, alternatively at least 600 frames per second.

The CPU can process at a rate of 100 frames per second, alternatively greater than 200 frames per second, alternatively greater than 600 frames per second.

The results of the image analysis, when compared to criteria pre-programmed into processor 50, may result in a desired treatment of skin surface 18. For instance, when the calculated ΔL_(M) exceeds the pre-determined ΔL_(S), a signal is sent from processor 50 to cartridge 52, via cartridge line 51, to fire one or more nozzles 21 in nozzle array 20 and dispense the cosmetic ink composition.

Power for cartridge 52, light 44, sensor 46, processor 50, and other mechanical and electrical elements that might be present can be supplied by power element 54 via one or more power lines 55. Power element 54 can be turned off and on, which in turn turns personal care device 40 off and on, via power switch 56 which can be located anywhere on personal care device 40, but is shown here on device cover 58. Power element 54 may include energy storage functionality via a battery, a rechargeable battery, an electrochemical capacitor, a double-layer capacitor, a supercapacitor, a hybrid battery-capacitor system, and combinations thereof.

FIG. 2 shows an exploded view of cartridge 52 comprising cartridge cap 62 and cartridge body 64. Cartridge body 64 can include standpipe 66 which is typically enclosed within cartridge body 64 and defines nozzle outlet 68. Optional filter 70 can help keep excessively large particles, and other debris out of nozzle array 20. Filter 70 and nozzle array 20 can be on opposite sides of nozzle outlet 68. Cosmetic ink composition 74 can be contained within cartridge body 64. Foam core 72 can at least partially fill cartridge 64 and helps to regulate back pressure of cosmetic ink composition 74. Back pressure can be regulated via bladders (not shown) and other methods known to the art. Foam core 72 shown here is just one example of how to help regulate the flow of cosmetic ink composition 74 to standpipe 66 through filter 70 and into nozzle array 20. Connector 78 can provide the electrical power and signal to nozzle array 20. Cosmetic ink composition 74 may be ejected from the cartridge 52 by piezoelectric means, thermal means, mechanical pumping means, or a combination of these.

An exemplary cartridge for use herein can include cartridges described in Patent Application US 2002/0167566.

There is no technical difference between an image used for background L values and those used for local L values, the difference is in the analysis of the image. Hence, the images are continually sent to the processor to calculate the L values and ΔL_(M) values. By “sent” it is understood, that preferably at least 4 bits of data per pixel are transferred for each image, and preferably, this 4-bit (or more) packet of data is used in the calculation of each local L value.

It is understood, that the background L can be calculated once in a treatment period and that value can be reused throughout the treatment period. Alternatively, it can be continually recalculated as long as the treatment process goes on. Moreover, there can be pre-programmed triggers to initiate a recalculation of the background L. Also, the background L may be retrieved from the processor memory to be used for the current background L.

When the ΔL_(M) exceeds the predetermined value, the cosmetic ink composition can be deposited onto at least a portion of the skin imperfection. In particular, the cosmetic ink composition can be deposited via an array of nozzles and the local L can be calculated along the length of, and in the firing range of, the array of nozzles. An individual nozzle may be fired to deposit the cosmetic ink composition, or multiple nozzles can be fired at the same time. The number of nozzles fired along the array of nozzles can be adjusted based on the size of the ΔL_(M) and the size of the skin imperfection. Furthermore, the frequency of nozzle firing can be adjusted based on the ΔL_(M), with more droplets being fired in succession in response to larger ΔL_(M) values.

The personal care device may deposit the cosmetic ink composition in droplets having an average diameter of from about from about 0.1 μm to about 60 μm, alternatively from about 1 μm to about 50 μm, alternatively from about 5 μm to about 40 μm. Preferably, the cosmetic ink composition can be applied to the skin imperfection in a discontinuous pattern of discrete droplets.

The cosmetic ink composition can be printed from a cartridge having a micro-electro-mechanical system (MEMS) that is different from typical consumer printing applications. It is known that the typical chamber height and nozzle plate thicknesses are from about 25 to about 50 μm since typical printing inks have a viscosity of less than about 10 cP. In one aspect, the cartridge can comprise a chamber height and nozzle plate thicknesses of from about 10 to about 20 μm, preferably from about 12 to about 17 μm. Without being limited by theory it is believed that the shorter chamber height and plate thickness can help minimize viscous loss. In addition, most consumer printing applications are optimized for printing at 10 kHz or more, so ink formulas and microfluidics are designed to achieve rapid refill. However, operating the cosmetic ink composition described herein at this frequency range can result in streaming and/or de-priming due to gulping of air.

The cosmetic ink composition can be printed using the following start-up sequence: heating the substrate to about 60° C. for less than about 600 ms, firing the nozzles in a burst of from about 100 to about 500 fires at a frequency of about 300 to about 1000 Hz, and then maintaining the low shear condition with continuous 4 Hz firing. While it is possible the nozzles will start up with different algorithms, it is likely that the cosmetic ink composition would not be transitioned from its viscous at-rest state to a flowing state.

Also described herein is a method for depositing the cosmetic ink composition onto skin. The method for depositing a cosmetic ink composition onto skin can comprise the steps of:

-   -   a. providing a personal care device comprising one or more         nozzles and a cartridge operatively associated with the one or         more nozzles, wherein a cosmetic ink composition is disposed         within the cartridge; and     -   b. depositing the cosmetic ink composition onto a portion of         skin, wherein the cosmetic ink composition is deposited in a         discontinuous droplet pattern.

More specifically, a method for depositing a cosmetic ink composition onto skin can comprise the steps of:

-   -   a. providing a personal care device comprising an array of         nozzles;     -   b. providing a background lightness (L) value;     -   c. obtaining a treatment image of skin and calculating at least         one local L value of individual pixels or group of pixels within         the treatment image;     -   d. comparing the local L value to the background L value;     -   e. identifying a skin deviation where the absolute value of the         difference between the local L value and the background L value         is greater than a predetermined set delta L value; and treating         the skin deviation with a cosmetic ink composition;         wherein the ink composition comprises a particulate material         having a Particle Size Distribution D50 of about 100 nm to about         2,000 nm; a (meth)acrylic acid homopolymer or salt thereof         having a weight average molecular weight of less than about         20,000 daltons; and a rheology modifier, wherein the rheology         modifier is selected from the group consisting of alkali         swellable emulsion polymers, hydrophobically modified alkali         swellable emulsion polymers, and combinations thereof; and         wherein the ink composition has a first dynamic viscosity of         greater than about 1,100 cP at a shear rate of 0.1 sec⁻¹         measured at 25° C. and a second dynamic viscosity of less than         about 100 cP at a shear rate of 1,000 sec⁻¹ measured at 25° C.

Examples and Data

The following data and examples, including comparative examples, are provided to help illustrate cosmetic ink compositions described herein. The exemplified compositions are given solely for the purpose of illustration and are not to be construed as limitations of the present invention, as many variations thereof are possible without departing from the spirit and scope of the invention. All parts, percentages, and ratios herein are by weight unless otherwise specified.

A series of formulas were prepared in a fractional factorial study design to understand the effect of the level of (meth)acrylic acid homopolymer or salt thereof and rheology modifier in the formula. Examples 1-18 were made according to the procedure described hereafter. The level of Polyvinylpyrrolidone/vinyl acetate (PVP/VA) and 1,2 Hexanediol/Caprylyl Glycol (commercially available as Symdiol® from Symrise AG, Branchburg, N.J.) was kept constant at 1%, respectively. The level of total particulate material, propylene glycol, (meth)acrylic acid homopolymer sodium polyacrylate (Darvan® 811D), and HASE type rheology modifier (ACULYN™ Excel, available from The Dow Chemical Company, Lake Zurich, Ill.) were varied. Example 4 is a control containing no (meth)acrylic acid homopolymer or salt thereof.

The samples were stored in sealed glass jars at 50° C. until measurements were performed. Samples were tested to determine the optimal level of (meth)acrylic acid homopolymer or salt thereof and rheology modifier by measuring the amount of separation. The measurement of separation at 50° C. was used as a screening tool to understand which formulas could build sufficient internal structure to suspend the particles. Samples that exhibit a large change in particle size distribution and/or particle settling separation suggest that the formulations are unstable.

Examples 1-18 were made according to the following formulas. Weight percent is shown as added.

TABLE 1 1 2 3 4 5 6 Phase Description Wt. % Wt. % Wt. % Wt. % Wt. % Wt. % A 75 wt % TiO₂ Slurry (WPG75PFSP)¹ 12.18 12.18 12.18 12.18 18.81 5.55 A 45 wt % Iron Oxide Slurry (WPG45GYSP)¹ 1.78 1.78 1.78 1.78 2.76 0.81 A 55 wt % Iron Oxide Slurry (WPG55GRSP)¹ 0.11 0.11 0.11 0.11 0.17 0.05 B Deionized Water 60.06 60.06 57.53 61.73 50.99 66.32 B PuraGuard ™ Propylene Glycol² 20.00 20.00 20.00 20.00 20.00 20.00 B 50 wt % PVP/VA 735W³ in water 1.00 1.00 1.00 1.00 1.00 1.00 B Symdiol ® 68⁴ 1.00 1.00 1.00 1.00 1.00 1.00 C 5 wt % Darvan ® 811D⁵ in water 2.20 2.20 4.20 0.00 2.20 2.20 D 15 wt % ACULYN ™ Excel⁶ in water 1.67 1.67 2.20 2.20 3.07 3.07 7 8 9 10 11 12 Phase Description Wt. % Wt. % Wt. % Wt. % Wt. % Wt. % A 75 wt % TiO₂ Slurry (WPG75PFSP)¹ 15.58 15.58 8.79 8.79 8.45 8.45 A 45 wt % Iron Oxide Slurry (WPG45GYSP)¹ 2.28 2.28 1.29 1.29 1.24 1.24 A 55 wt % Iron Oxide Slurry (WPG55GRSP)¹ 0.14 0.14 0.08 0.08 0.07 0.07 B Deionized Water 46.80 67.74 56.64 73.58 79.65 48.17 B PuraGuard ™ Propylene Glycol² 29.47 10.53 29.47 10.53 3.46 36.54 B 50 wt % PVP/VA 735W³ in water 1.00 1.00 1.00 1.00 1.00 1.00 B Symdiol ® 68⁴ 1.00 1.00 1.00 1.00 1.00 1.00 C 5 wt % Darvan ® 811D⁵ in water 3.20 1.20 1.20 3.20 3.00 1.40 D 15 wt % ACULYN ™ Excel⁶ in water 0.53 0.53 0.53 0.53 2.13 2.13 13 14 15 16 17 18 Phase Description Wt. % Wt. % Wt. % Wt. % Wt. % Wt. % A 75 wt % TiO₂ Slurry (WPG75PFSP)¹ 21.95 21.95 2.41 2.41 15.91 15.91 A 45 wt % Iron Oxide Slurry (WPG45GYSP)¹ 3.22 3.22 0.35 0.35 2.33 2.33 A 55 wt % Iron Oxide Slurry (WPG55GRSP)¹ 0.20 0.20 0.02 0.02 0.14 0.14 B Deionized Water 55.25 42.69 62.77 79.83 37.95 72.63 B PuraGuard ™ Propylene Glycol² 12.72 27.28 27.78 12.72 36.54 3.46 B 50 wt % PVP/VA 735W³ in water 1.00 1.00 1.00 1.00 1.00 1.00 B Symdiol ® 68⁴ 1.00 1.00 1.00 1.00 1.00 1.00 C 5 wt % Darvan ® 811D⁵ in water 3.20 1.20 3.20 1.20 3.00 1.40 D 15 wt % ACULYN ™ Excel⁶ in water 1.47 1.47 1.47 1.47 2.13 2.13 ¹Supplied by KOBO Products Inc (South Plainfield, NJ). ²Available from The Dow Chemical Company (Lake Zurich, IL). ³Available from Ashland Specialty Chemical (Wilmington, DE). ⁴Available from Symrise AG (Branchburg, NJ). ⁵Sodium polyacrylate available from Vanderbilt Minerals LLC (Norwalk, CT). ⁶Polyacrylate available from The Dow Chemical Company (Lake Zurich, IL).

The table below shows the viscosity, PSD D50, and separation for each example. Properties such as viscosity, Particle Size Distribution (PSD), separation, loss modulus, and/or storage modulus can be used to evaluate whether the cosmetic ink composition can be stable and jettable. Viscosity was measured after approximately 1 week from formulation and PSD D50 was measured after formulation and again after 4 weeks. Viscosity was measured according to the Viscosity Test Method described hereafter. PSD was measured according to the Particle Size Distribution Method described hereafter. Separation was measured according to the Separation Test Method described hereafter. Separation is recorded in Table 2 as the number of days it took for the sample to reach 2 mm of separation, with the type of separation noted.

TABLE 2 First Wt % (Active) Dynamic Total Viscosity PSD D50 Separation at Particulate Propylene Rheology Sodium 0.1 sec⁻¹ (nm) 50° C. Ex Material Glycol Modifier Polyacrylate cP T = 0 T = 4 wks Days Type 1 10.00 20.00 0.25 0.11 1230 250 230 1 Syneresis 2 10.00 20.00 0.25 0.11 1430 260 240 1 Syneresis 3 10.00 20.00 0.33 0.21 1810 240 270 5 Syneresis 4 10.00 20.00 0.33 0.00 29400 670 1,000 20 Syneresis 5 15.44 20.00 0.46 0.11 9120 280 260 24 Syneresis 6 4.56 20.00 0.46 0.11 4950 230 240 24 Syneresis 7 12.79 29.47 0.08 0.16 165 260 230 1 Settling 8 12.79 10.53 0.08 0.06 132 230 240 1 Settling 9 7.21 29.47 0.08 0.06 12 240 230 1 Settling 10 7.21 10.53 0.08 0.16 3 270 230 0 Settling 11 6.94 3.46 0.32 0.15 1130 240 270 5 Syneresis 12 6.94 36.54 0.32 0.07 3920 230 250 14 Syneresis 13 18.02 12.72 0.22 0.16 590 240 240 1 Settling 14 18.02 27.28 0.22 0.06 2780 230 270 2 Syneresis 15 1.98 27.28 0.22 0.16 333 260 230 0 Settling 16 1.98 12.72 0.22 0.06 391 250 220 0 Settling 17 13.06 36.54 0.32 0.15 2880 240 240 11 Syneresis 18 13.06 3.46 0.32 0.07 3770 270 250 15 Syneresis

It was found that the most stable formulas contained 0.32 active wt % rheology modifier or more. Examples 3-6, 11-12, and 17-18, which comprised 0.32 active wt % rheology modifier or greater, each had a first dynamic viscosity of greater than 1,100 cP and took 5-24 days to reach 2 mm of separation with syneresis observed, demonstrating that the formulas could build a sufficient internal structure to keep the particles in suspension. Without being limited by theory, it is believed that a sample demonstrating syneresis can still be stable because the particles are uniformly distributed below the clear fluid layer. In contrast, separation with settling in which the particles fall to the bottom of the sample may not be stable as the internal structure of the sample is not sufficient to suspend the particles.

Examples 3 and 4 demonstrate the need for both the rheology modifier and the (meth)acrylic acid homopolymer sodium polyacrylate to achieve a viscosity and particle size suitable for jetting while maintaining particle suspension. Examples 3 and 4 comprised 0.33 active wt % rheology modifier and a constant level of total particulate material and propylene glycol. However, Example 3 had 0.21 active wt % (meth)acrylic acid homopolymer sodium polyacrylate while Example 4 had no (meth)acrylic acid homopolymer or salt thereof. Example 4 had better separation control as compared to Example 3; however, Example 4 exhibited a first dynamic viscosity of 29,400 cP and poor control of particle size over 4 weeks as demonstrated by the increase in PSD D50. It is believed that the particle size and viscosity of Example 4 would not be suitable for jetting.

Examples 5 and 6 had a constant level of propylene glycol, rheology modifier, and (meth)acrylic acid homopolymer sodium polyacrylate, but varied the level of total particulate material. Example 5 had a higher level of total particulate material as compared to Example 4 and demonstrated a higher viscosity. However, both Example 5 and 6 took 24 days to reach 2 mm of separation. Without being limited by theory, it is believed that the level of (meth)acrylic acid homopolymer or salt thereof and rheology modifier needed for particle size control and particle suspension may not depend on the particulate material level. It is believed that as long as the rheology modifier is present with some amount of particulate material, a weak colloidal gel can be formed.

In a separate experiment, different formulas were prepared to further assess the impact of the (meth)acrylic acid homopolymer or salt thereof and rheology modifier on the viscosity and separation of the cosmetic ink composition. Examples 19-22 were made according to the procedure described hereafter. Example 19 illustrates a cosmetic ink composition containing a (meth)acrylic acid homopolymer sodium polyacrylate (Darvan® 811D) and a HASE type rheology modifier (ACULYN™ Excel). Example 20 is a comparative example containing no rheology modifier. Example 21 is a comparative example containing no (meth)acrylic acid homopolymer or salt thereof. Example 22 is a comparative example containing a C12/C14 amine oxide as the rheology modifier.

Examples 19-22 were made according to the following formulas. Weight percent is shown as added.

TABLE 3 19 20 21 22 Phase Description wt % wt % wt % wt % A 75 wt % TiO₂ Slurry (WPG75PFSP)¹ 12.18 11.54 12.18 15.81 A 45 wt % Iron Oxide Slurry 1.78 2.82 1.78 2.31 (WPG45GYSP)¹ A 55 wt % Iron Oxide Slurry 0.11 0 0.11 0 (WPG55GRSP)¹ A 45 wt % Iron Oxide Slurry 0 0.14 0 0.20 (WPG45SIRSP)¹ B Deionized Water 57.53 60.30 61.73 53.98 B PuraGuard ™ Propylene Glycol² 20.00 20.00 20.00 22.00 B 50 wt % PVP/VA 735W³ copolymer 1.00 0 1.00 0 in water B Symdiol ® 68⁴ 1.00 1.00 1.00 0 C 5 wt % Darvan ® 811D⁵ in water 4.20 4.20 0 2.90 D 15 wt % ACULYN ™ Excel⁶ 2.20 0 2.20 0 in water D 15% C12/C14 Amine Oxide⁷ 0 0 0 2.80 ¹Supplied by KOBO Products Inc (South Plainfield, NJ). ²Available from The Dow Chemical Company (Lake Zurich, IL). ³Available from Ashland Specialty Chemical (Wilmington, DE). ⁴Hexanediol/Caprylyl Glycol available from Symrise AG (Branchburg, NJ). ⁵Sodium polyacrylate available from Vanderbilt Minerals LLC (Norwalk, CT). ⁶Polyacrylate available from The Dow Chemical Company (Lake Zurich, IL). ⁷Available from The Dow Chemical Company (Lake Zurich, IL).

The samples were stored in sealed glass jars at 50° C. until measurements were performed. The table below shows the PSD, viscosity, tan(delta), and separation for each example. Example 22 was tested at a different time; however, the data are shown together for ease of comparison. PSD is measured according to the Particle Size Distribution Method described hereafter. Viscosity was measured according to the Viscosity Test Method described hereafter. Tan(delta) was calculated by using the storage modulus and loss modulus measured according to the Oscillatory Strain Sweep Method described hereafter. Separation was measured according to the Separation Test Method described hereafter. Separation is recorded in Table 4 as the number of days it took for the sample to reach 2 mm of separation, with the type of separation noted.

TABLE 4 Rheology First Second Modifier Sodium PSD PSD Dynamic Dynamic Separation at wt % Polyacrylate D50 D90 Viscosity Viscosity tan 50° C. Ex (active) wt % (active) (nm) (nm) 0.1 s⁻¹ (cP) 1000 s⁻¹ (cP) delta Days Type 19 0.33 0.21 390 660 1810 35 0.62 5 Syneresis 20 0 0.21 390 640 125 2 4.11 <1 Settling 21 0.33 0 1730 3560 29400 91 0.21 20 Syneresis 22 0.42 0.145 4440 1200 110 4 5.17 2 Settling

Example 19, which contained 0.33 active wt % HASE rheology modifier and 0.21 active wt % (meth)acrylic acid homopolymer sodium polyacrylate, had a first dynamic viscosity of 1,810 cP and a second dynamic viscosity of 35 cP, demonstrating that the formula had shear thinning behavior. In addition, Example 19 had agglomeration control as the PSD D90 was maintained under 1 μm. Finally, Example 19 had a tan(delta) below 1 and took 5 days to reach 2 mm of separation with syneresis observed.

Comparative Example 20, which contained 0.21 active wt % (meth)acrylic acid homopolymer sodium polyacrylate and no rheology modifier, had a particle size distribution D90 under 1 μm. However, Comparative Example 20 had a first dynamic viscosity of only 125 cP and was not as shear thinning as compared to Example 19. Comparative Example 20 reached 2 mm of separation in less than 1 day with settling observed. It is believed that without the rheology modifier, the formula could not build enough viscosity to suspend the particles.

It has been previously reported that the HASE rheology modifier ACULYN™ Excel can provide a thixotropic ink composition that is jettable. However, it was found that although Comparative Example 21, which contained 0.33 active wt % ACULYN™ Excel HASE rheology modifier and no (meth)acrylic acid homopolymer sodium polyacrylate, had shear thinning behavior and good separation control at 50° C., it had a PSD D50 4.4 times greater than Example 19, indicating poor particle size control. Comparative Example 21 had a PSD D50 of 1730 nm and a PSD D90 of 3560 nm. It is known that the microfluidic channels in ink cartridges can be very small, for example about from about 10 μm to about 25 μm. As such, it is believed that Comparative Example 21 would likely be difficult to refill in a standard printer ejection head because of the high viscosity and would likely clog the flow channels due to the presence of larger particles. It is also believed that the particles in Comparative Example 21 may not have the optimal size for opacity.

Comparative Example 22 contained 0.42 active wt % C12/C14 amine oxide rheology modifier and 0.145 active wt % (meth)acrylic acid homopolymer sodium polyacrylate. It has been previously reported amine oxides may provide some yield stress and may help prevent settling of particles in a cosmetic ink composition. However, it was surprisingly found that C12/C14 amine oxide in Comparative Example 22 did not build viscosity to the same extent as Example 19 and reached 2 mm of separation in only 2 days with settling observed, demonstrating that C12/C14 in this formula is not able to build sufficient viscosity to suspend the particles.

Rheology Modifier Study

Different formulas were tested to assess the impact of rheology modifiers on particle settling. Base Formula 1 was prepared as described hereinafter. Various rheology modifiers (see Table 6) were then added to Base Formula 1 to form Examples 23-35. Propylene Glycol was added to Base Formula 1 as a control (Example 35). Examples 23-35 were prepared as described hereinafter. Approximately 30 mL of the resulting mixture was placed into a 40 mL vial and stored at ambient conditions.

Base Formula 1 was made according to the following formula. Weight percent is shown as added.

TABLE 5 Phase Ingredient wt % A 75 wt % TiO₂ Slurry (WPG75PFSP)¹ 22.50 A 45 wt % Iron Oxide Slurry (WPG45GYSP)¹ 3.30 A 55 wt % Iron Oxide Slurry (WPG55GRSP)¹ 0.20 B Deionized Water 46.00 B PuraGuard ™ Propylene Glycol² 12.50 B 50 wt % Polyvinylpyrrolidone/vinyl acetate (PVP) 1.50 735W³ in water B Symdiol ® 68⁴ 1.00 C Deionized Water 10.00 D 5 wt % Darvan ® 811D⁵ in water 3.00 Total 100.00 ¹Supplied by KOBO Products Inc (South Plainfield, NJ). ²Available from The Dow Chemical Company (Lake Zurich, IL). ³Available from Ashland Specialty Chemical (Wilmington, DE). ⁴1,2 Hexanediol/Caprylyl Glycol available from Symrise AG (Branchburg, NJ). ⁵Sodium polyacrylate available from Vanderbilt Minerals LLC (Norwalk, CT).

Examples 23-35 were held for 4 days at ambient conditions. Particle settling was assessed for each example by measuring weight percent solids at the top, middle, and bottom of the sample according to the Particle Settling Test Method described hereafter. Weight percent solids is recorded in table 6 as the solids remaining after drying the volatiles off.

The table below summarizes the results.

TABLE 6 Weight Percent Solids wt % Bottom Middle Top Ex Rheology Modifier (active) Chemical Type (wt %) (wt %) (wt %) 23 ACRYSOL ™ TT615² 0.2 HASE 45.0 1.0 1.0 24 ACRYSOL ™ TT615² 0.4 HASE 14.3 14.4 5.5 25 ACRYSOL ™ TT615² 0.6 HASE 18.0 16.3 15.9 26 ACULYN ™ Excel⁶ 0.4 HASE/acrylates 18.1 17.8 17.7 copolymer 27 ACULYN ™ 38² 0.4 ASE/acrylates 57.1 1.3 1.8 niodecanoate crosspolymer 28 ACRYSOL ™ TT935² 0.2 HASE 42.9 1.2 1.3 29 ACRYSOL ™ TT935² 0.4 HASE 26.9 1.4 1.2 30 ACRYSOL ™ TT935² 0.6 HASE 16.0 1.8 2.1 31 Natrosol ™ 250 HHR⁸ 0.4 Hydroxyethyl cellulose 24.4 2.6 1.2 32 Stabylen 30⁹ 0.2 Acrylates/Vinyl 21.9 10.3 3.2 Isodecanoate Crosspolymer 33 Carbopol ® Ultrez 21¹⁰ 0.2 Hydrophobically modified 17.9 12.0 4.1 crosslinked polyacrylate 34 Aristoflex ® HMB¹¹ 0.5 Ammonium 43.2 3.9 2.6 Acryloyldimethyltaurate/ Beheneth- 25 Methacrylate Crosspolymer 35 PuraGuard ™ 10.0 Glycol 20.9 14.9 2.0 Propylene Glycol² ²Available from The Dow Chemical Company (Lake Zurich, IL). ⁶Polyacrylate available from The Dow Chemical Company (Lake Zurich, IL). ⁸Available from Ashland (Covington, KY). ⁹Available from 3V Sigma (Georgetown, SC). ¹⁰Available from Lubrizol (Wickliffe, OH). ¹¹Available from Clariant Corp. (Blue Ash, OH).

It was found that Example 23, which contained 0.2 active wt % ACRYSOL™ TT615, did not build sufficient viscosity and particle settling took place over the 4 day period, as demonstrated by the differing weight percent solids content from top to bottom. However, it was found that as the concentration of ACRYSOL™ TT615 increased, particle settling stability increased. Examples 24 and 25, which comprised 0.4 and 0.6 active wt % ACRYSOL™ TT615, respectively, built sufficient viscosity and the particles did not significantly settle over the 4 day period, although some syneresis was observed. It was found that the weight percent solids content from top to bottom was consistent for Example 26, indicating that the particles did not significantly settle over the 4 day period. Examples 26 comprised 0.4 active wt % of the HASE polymer ACULYN™ Excel. It was found that the Example 28-30 formulations, which comprised the HASE class polymer ACRYSOL™ TT935, were not able to build sufficient viscosity within the composition and solids settling took place over the 4 day period. Without being limited by theory, it is believed that this particular HASE polymer may not have sufficient charge density and may have too much hydrophobicity to build the viscosity needed to maintain stability and limit particle settling. However, it is believed that at higher concentrations this rheology modifier may be able to thicken the cosmetic ink composition and build a sufficient viscosity to suspend the particles. Example 27, which comprised the ASE class polymer ACULYN™ 38 showed substantial particle settling over the 4 day period. It is believed that adjusting the level of ACULYN™ 38 ASE polymer can improve the suspension of solids and reduce the particle settling. Finally, Examples 31-35 are comparative examples which showed substantial variation in the solids content from top to bottom indicating that particle settling took place over the 4 day period.

In a separate study, different formulas were tested to assess the impact of various types of ASE, HASE, and HEUR polymer rheology modifiers on viscosity and separation of the cosmetic ink composition. Examples 36-48 were prepared according to the procedure described hereinafter.

Examples 36-48 were made according to the formulas in the tables below. Weight percent is shown as added.

TABLE 7 36 37 38 39 40 Phase Ingredient wt % wt % wt % wt % wt % A 75 wt % TiO2 Slurry (WPG75PFSP)¹ 18.46 18.46 15.00 15.00 15.00 A 45 wt % Iron Oxide Slurry (WPG45GYSP)¹ 4.51 4.51 3.67 3.67 3.67 A 45 wt % Iron Oxide Slurry (WPG45SIRSP)¹ 0.29 0.29 0.22 0.22 0.22 A Deionized Water 10.00 10.00 10.00 10.00 10.00 B Deionized Water 37.8 37.14 43.51 40.51 39.90 B PuraGuard ™ Propylene Glycol² 23.00 23.00 23.00 23.00 23.00 C 5 wt % Darvan ® 811D⁵ in water 2.60 2.60 2.60 4.00 4.00 D 15 wt % ACRYSOL ™ TT615² in water 3.33 0 0 0 0 D 15 wt % Rheovis ® AS1125¹² in water 0 3.33 0 0 0 D 15 wt % ACULYN ™ Excel⁶ in water 0 0 2.00 0 0 D 15 wt % ACULYN ™ 22² in water 0 0 0 3.60 0 D 15 wt % ACULYN ™ 33² in water 0 0 0 0 3.93 41 42 43 44 45 Phase Ingredient wt % wt % wt % wt % wt % A 75 wt % TiO2 Slurry (WPG75PFSP)¹ 15.00 15.00 15.00 15.00 15.00 A 45 wt % Iron Oxide Slurry (WPG45GYSP)¹ 3.67 3.67 3.66 3.66 3.66 A 45 wt % Iron Oxide Slurry (WPG45SIRSP)¹ 0.22 0.22 0.22 0.22 0.22 A Deionized Water 10.00 10.00 10.00 10.00 10.00 B Deionized Water 40.31 39.11 39.60 40.52 37.72 B PuraGuard ™ Propylene Glycol² 23.00 23.00 23.00 23.00 23.00 C 5 wt % Darvan ® 811D⁵ in water 4.00 4.00 4.00 4.00 4.00 D 15 wt % ACULYN ™ 38² in water 3.80 0 0 0 0 D 15 wt % ACULYN ™ 88² in water 0 5.00 0 0 0 D 15 wt % Rheovis ® 1152¹² in water 0 0 4.53 0 0 D 15 wt % Rheovis ® 1156¹² in water 0 0 0 3.60 0 D 15 wt % ACRYSOL ™ TT935² in water 0 0 0 0 6.40 46 47 48 Phase Ingredient wt % wt % wt % A 75 wt % TiO2 Slurry (WPG75PFSP)¹ 15.00 15.00 15.00 A 45 wt % Iron Oxide Slurry (WPG45GYSP)¹ 3.66 3.66 3.66 A 45 wt % Iron Oxide Slurry (WPG45SIRSP)¹ 0.22 0.22 0.22 A Deionized Water 10.00 10.00 10.00 B Deionized Water 40.26 32.18 32.18 B PuraGuard ™ Propylene Glycol² 23.00 23.00 23.00 C 5 wt % Darvan ® 811D⁵ in water 4.00 2.60 2.60 D 15 wt % ACRYSOL ™ DR300² solution 3.86 0 0 D 15 wt % ACULYN ™ 44² in water 0 12.40 0 D 15 wt % ACULYN ™ 46N² in water 0 0 12.47 ¹Supplied by KOBO Products Inc (South Plainfield, NJ). ²Available from The Dow Chemical Company (Lake Zurich, IL). ⁵Sodium polyacrylate available from Vanderbilt Minerals LLC (Norwalk, CT). ⁶Polyacrylate available from The Dow Chemical Company (Lake Zurich, IL). ¹²Available from BASF (Florham Park, NJ).

The samples were stored in sealed glass jars at 25° C. or 40° C. until measurements were performed. The table below shows the viscosity, tan(delta), and separation measured 11 days after formulation for each example. Viscosity was measured according to the Viscosity Test Method described hereafter. Tan(delta) was calculated using the storage modulus and loss modulus measured according to the Oscillatory Strain Sweep Method described hereafter. Separation was measured according to the Separation Test Method described hereafter.

TABLE 8 Rheology Modifier Sodium Viscosity Separation at 11 days wt % Polyacrylate 0.1 s⁻¹ 1000 s⁻¹ tan 25° C. 40° C. Ex Name Type (active) wt % (active) (cP) (cP) (delta) (mm) (mm) Type 36 ACRYSOL ™ HASE 0.50 0.13 6290 76 0.61 1 16 Syneresis TT615 37 Rheovis ® ASE 0.50 0.13 2040 73 0.68 2 3 Syneresis AS1125 38 ACULYN ™ HASE 0.30 0.13 3180 37 0.54 0 0 none Excel 39 ACULYN ™ HASE 0.54 0.2 4670 71 0.43 0 14 Syneresis 22 40 ACULYN ™ ASE 0.59 0.2 4040 63 0.41 0 0 none 33 41 ACULYN ™ ASE 0.57 0.2 2280 42 0.49 0 1.5 Syneresis 38 42 ACULYN ™ HASE 0.75 0.2 4320 71 0.50 0.5 1.5 Syneresis 88 43 Rheovis ® HASE 0.68 0.2 3060 80 0.95 3.5 25 Syneresis 1152 44 Rheovis ® HASE 0.54 0.2 1290 69 1.77 21 40 Syneresis 1156 45 ACRYSOL ™ HASE 0.96 0.2 763 61 1.89 37 46 Syneresis TT935 46 ACRYSOL ™ ASE 0.58 0.2 624 43 1.64 43 49.5 Syneresis DR300 47 ACULYN ™ HEUR 1.86 0.13 194 22 3.30 46 49.5 Settling 44 48 ACULYN ™ HEUR 1.87 0.13 460 32 4.15 48 52 Settling 46N

For both ASE and HASE polymers, it is believed that the interaction of the anionic moiety of the rheology modifier with the particle surface and the (meth)acrylic acid homopolymer or salt thereof can promote stability. This forms a weak colloidal gel by introducing elasticity in the composition (as demonstrated by the storage modulus of the cosmetic ink composition) along with viscosity (as demonstrated by the loss modulus of the cosmetic ink composition). Particle suspension can be achieved for cosmetic ink compositions having a low ratio of G″ to G′, i.e. a tan(delta) of preferably less than about 1, more preferably less than about 0.60.

It was found that Examples 36-43, which all had a first dynamic viscosity of greater than 1,100 cP and a tan(delta) of less than 1, had less than 4 mm of separation at 11 days at 25° C. with syneresis observed. Under accelerated temperature conditions, Examples 36-43 had 25 mm of separation or less at 11 days with syneresis observed. Examples 38 and 40 had no separation at 11 days under both temperature conditions tested.

Although Example 44 had a first dynamic viscosity of 1,290 cP that falls within the preferred range, the tan(delta) was greater than 1 and 21 mm of separation was observed at 11 days. Examples 45 and 46 contained HASE and ASE type rheology modifiers, respectively. However, Examples 45 and 46 were not able to build a sufficient viscosity to suspend the particles, as demonstrated by the first dynamic viscosity of well below 1,100 cP and the mm of separation at both temperature conditions. Without being limited by theory, it is believed that these formulas were not able to form a strong enough colloidal gel to keep the particles in suspension because the formulations comprised too many hydrophobic moieties. Finally, Examples 47 and 48, which contained HEUR type rheology modifiers, had a first dynamic viscosity of less than 500 cP and a tan(delta) of well above 1. Examples 47 and 48 were not able to build sufficient viscosity to suspend the particles and had over 45 mm of separation at 11 days with particle settling observed under both temperature conditions. Not wishing to be bound by theory, it is believed that HEUR polymers may not be able to build sufficient elasticity and/or viscosity in the cosmetic ink composition to keep the particles suspended.

Examples 1-22 were made according to the following procedure.

First, the ingredients of Phase A were combined in an appropriate premix container and mixed for 30 minutes. The ingredients of Phase B were added into a main container. Phase B was mixed using a mixer with a propeller blade, such as a digital Eurostar 400® available from IKA® (Staufen im Breisgau, Germany) or equivalent, at low speed until the mixture was homogenous. The pH of the Phase B mixture was measured. Then, the contents of the premix container were transferred into the main container and mixed for 30 minutes. Approximately 10% of the water was withheld from Phase B and was used to wash the premix container and then added to the main container while mixing. Phase C was added to the main container. The mixing speed was increased to high speed and mixing continued for 10 minutes. Phase D was then added dropwise to the main container and the pH was maintained between 7.5-8.5 by adding 20% KOH. Homogeneity was ensured and the mixture was poured into a container, labeled, and stored at ambient conditions before use.

Examples 23-35 were made according to the following procedure.

First, Base Formula 1 was prepared. The ingredients of Phase A were combined in an appropriate premix container. The ingredients of Phase B were added into a main container. Phase B was mixed using a mixer with a propeller blade, such as a digital Eurostar 400® available from IKA® (Staufen im Breisgau, Germany), or equivalent, at low speed until the mixture was homogenous. While mixing, Phase A was added into the main container. Phase C was added to the premix container to wash out the container and then added to the main container while mixing continued. The mixing speed was increased to high speed and mixing continued for 10 minutes. Phase D was then added to the main container and mixed for 15 minutes to form Base Formula 1. Homogeneity was ensured and Base Formula 1 was poured into a container. In separate containers, the rheology modifiers were prepared as solution in water. Each rheology modifier was premixed in deionized water at 15 wt % and then added to Base Formula 1 at the active wt % levels described in table 6 while adjusting the pH to approximately 8 with 20% KOH.

Examples 36-48 were prepared according to the following procedure.

First, the ingredients of Phase A were combined in an appropriate premix container and mixed for 30 minutes. The ingredients of Phase B were added into a main container. Phase B was mixed using a mixer with a propeller blade, such as a digital Eurostar 400® available from IKA® (Staufen im Breisgau, Germany) or equivalent, at low speed until the mixture was homogenous. The pH of the Phase B mixture was measured. Then, the contents of the premix container were then transferred into the main container and mixed for 30 minutes. Phase C was added to the main container and mixed. The pH of the main container was measured. Phase D was added to the main container dropwise and the pH was maintained between 7.5-8.5 by adding 20% KOH solution. Homogeneity was ensured and the mixture was poured into a container, labeled, and stored at ambient conditions before use.

Particle Size Distribution Method

The particle size distribution is determined using a laser scattering particle size distribution analyzer. A suitable laser scattering particle size distribution analyzer can include a Horiba LA-950V2 (available from Horiba, Ltd., Kyoto, Japan). In this method, the principles of Mie and Fraunhofer scattering theories are used to calculate the size and distribution of particles suspended in a liquid. Results are normally displayed on a volume basis. The application of this method to pigments has been developed using a flow cell procedure.

Samples are prepared by vortexing for 30 seconds with a Vortex Genie 2 to ensure there is no residue in the bottom of the sample vial. 200 mL of deionized (DI) water is added into the instrument reservoir and analyzed as a blank sample. A disposable micro pipet is used to dispense enough sample into the DI water in the instrument until the Transmittance is reduced from 100 down to 90±2%, approximately 250 μL. Results are reported as D50 or D90.

Viscosity Test Method

Viscosity is measured using a rheometer as a function of shear rate. A suitable rheometer can include an Ares M (available from TA Instruments, New Castle, Del.), or equivalent. First, the samples and standards are equilibrated at room temperature prior to analysis. A 50 mm, 2 degree, cone and plate is zeroed prior to testing. While the sample is at 25° C.±0.5° C., the sample is tested. A shear sweep measurement is performed over a range of 0.1-1000 s⁻¹ to determine the shear thinning properties and viscosity at different shear rates.

Separation Test Method

Separation is measured by filing an 8-dram (1 oz., 25 mm×95 mm) screw cap glass vial to a height of 55 mm with the sample composition (as measured from the bottom of the vial to the top of the liquid composition). The vials are sealed and are placed in controlled temperature chambers. The vials are held static storage until measurements are performed. At each time point, the vial is carefully removed from the chamber without vigorous or prolonged agitation and observed for any visual signs of separation and the type of separation is noted as syneresis or settling. The amount of separation is determined by measuring the mm of clear fluid at the top of the sample with a digital caliper.

Particle Settling Test Method

Particle settling is measured as follows. An aluminum dish is weighed to determine the dish weight. A 1 gram aliquot of the sample from the top, middle, or bottom of the sample vial is added to the dish and weighed to determine the wet weight. “Top” means the surface of the sample in the vial. “Middle” means the middle of the vial. “Bottom” means the bottom of the vial. The dish with the sample aliquot is placed in an oven at 100° C. for one hour to evaporate the volatiles. The dish is removed and weighed again to get a dry weight. The weight % solids is calculated by the following equation: (dry weight−dish weight)/(wet weight−dish weight).

Oscillatory Strain Sweep Method

Oscillatory strain sweep is measured using a rheometer (such as an ARES-G2 available from TA Instruments, New Castle, Del.), or equivalent.

The samples and standards are allowed to equilibrate at ambient conditions prior to analysis. The rheometer is calibrated as disclosed in the operator's manual. The oscillatory strain sweep measurement is performed at a fixed angular frequency of 6.28 rad/s over a strain range of 0.0001-1 using a 40 mm 316SST (APS heat break) parallel plate at 25° C., with a 0.05 mm gap, to determine the storage and loss moduli.

Zeta Potential Test Method

Zeta potential is measured using a Zeta potential analyzer such as a NanoBrook ZetaPALS Potential Analyzer available from Brookhaven Instruments Corporation, Holtsville, N.Y., or equivalent.

Zeta potential test samples are prepared by diluting the sample to 0.1 g/ml into deionized water. Zeta potential is measured on a Zeta potential analyzer using the Smoluchowski Zeta potential model with 5 runs and 10 cycles. After running a standard (BIZR3), the cells of the Zeta potential analyzer are loaded with 1 ml of test sample. Zeta potential is measured as a function of pH.

Combinations

-   -   A. A cosmetic ink composition comprising: from about 1% to about         30 active wt % of a particulate material having a Particle Size         Distribution D50 of 100 nm to 2,000 nm; a (meth)acrylic acid         homopolymer or salt thereof having a weight average molecular         weight of less than 20,000 daltons; and a rheology modifier,         wherein the rheology modifier is selected from the group         consisting of alkali swellable emulsion polymers,         hydrophobically modified alkali swellable emulsion polymers, and         combinations thereof; wherein the cosmetic ink composition has a         first dynamic viscosity of greater than 1,100 cP at a shear rate         of 0.1 sec⁻¹ measured at 25° C. and a second dynamic viscosity         of less than 100 cP at a shear rate of 1,000 sec⁻¹ measured at         25° C.     -   B. The cosmetic ink composition of paragraph A wherein the         cosmetic ink composition has a first dynamic viscosity of 1,100         cP to 10,000 cP at a shear rate of 0.1 sec⁻¹ measured at 25° C.,         preferably 1,500 cP to 8,000 cP, more preferably from 2,000 cP         to 5,000 cP, and a second dynamic viscosity of from 10 to 100 cP         at a shear rate of 1,000 sec⁻¹ measured at 25° C., preferably         from 20 to 80 cP.     -   C. The cosmetic ink composition of paragraph A or B, wherein the         cosmetic ink composition comprises greater than 0.30 active wt %         rheology modifier.     -   D. The cosmetic ink composition of any of the preceding         paragraphs comprising from 0.01 to 1 active wt % (meth)acrylic         acid homopolymer or salt thereof, preferably from 0.10 to 0.85         active wt %, more preferably from 0.20 to 0.75 active wt %.     -   E. The cosmetic ink composition of any of the preceding         paragraphs wherein cosmetic ink composition comprises a ratio of         (meth)acrylic acid homopolymer or salt thereof to rheology         modifier of from 0.1 to 0.75, preferably from 0.30 to 0.65.     -   F. The cosmetic ink composition of any of the preceding         paragraphs wherein the cosmetic ink composition further         comprises from 20 to 30 active wt % humectant.     -   G. The cosmetic ink composition of any of the preceding         paragraphs wherein the rheology modifier is an alkali swellable         acrylic polymer emulsion.     -   H. The cosmetic ink composition of any of the preceding         paragraphs wherein the (meth)acrylic acid homopolymer or salt         thereof is sodium polyacrylate.     -   I. The cosmetic ink composition of any of the preceding         paragraphs wherein the (meth)acrylic acid homopolymer or salt         thereof has a weight average molecular weight of from 2,000 to         5,000 daltons.     -   J. The cosmetic ink composition of any of the preceding         paragraphs wherein the cosmetic ink composition has a neat pH of         from 7.5 to 9.0.     -   K. The cosmetic ink composition of any of the preceding         paragraphs wherein the particulate material has a Particle Size         Distribution D50 of from 150 nm to 1,000 nm, preferably from 200         nm to 500 nm, and more preferably from about 200 nm to about 350         nm.     -   L. The cosmetic ink composition of any of the preceding         paragraphs the wherein particulate material has a Particle Size         Distribution D90 of from 700 nm to 900 nm.     -   M. The cosmetic ink composition of any of the preceding         paragraphs wherein the particulate material is selected from the         group consisting of a pigment, a metal oxide, a colorant, a dye,         a clay, and combinations thereof.     -   N. The cosmetic ink composition of any of the preceding         paragraphs wherein the cosmetic ink composition further         comprises one or more skin care actives selected from the group         consisting of niacinamide; inositol; undecylenoyl phenylalanine;         and combinations thereof.     -   O. The cosmetic ink composition of any of the preceding         paragraphs wherein the cosmetic ink composition further         comprises a preservative.     -   P. The cosmetic ink composition of any of the preceding         paragraphs further comprising a monohydric alcohol selected from         the group consisting of methanol, ethanol, 1-propanol,         2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol,         2-methyl-2-propanol and mixtures thereof.

Values disclosed herein as ends of ranges are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each numerical range is intended to mean both the recited values and any integers within the range. For example, a range disclosed as “1 to 10” is intended to mean “1, 2, 3, 4, 5, 6, 7, 8, 9, and 10.”

The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as “40 mm” is intended to mean “about 40 mm.”

Every document cited herein, including any cross referenced or related patent or application and any patent application or patent to which this application claims priority or benefit thereof, is hereby incorporated herein by reference in its entirety unless expressly excluded or otherwise limited. The citation of any document is not an admission that it is prior art with respect to any invention disclosed or claimed herein or that it alone, or in any combination with any other reference or references, teaches, suggests or discloses any such invention. Further, to the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern.

While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention. 

What is claimed is:
 1. A cosmetic ink composition comprising: a. from about 1 to about 30 active wt % of a particulate material; b. a (meth)acrylic acid homopolymer or salt thereof; and c. from about 0.3 to about 1 active wt % of a rheology modifier, wherein the rheology modifier is selected from the group consisting of a (meth)acrylate polymer, a (meth)acrylate copolymer, and mixtures thereof; wherein the cosmetic ink composition has a first dynamic viscosity of from about 1,100 cP to about 10,000 cP at a shear rate of 0.1 sec⁻¹ measured at 25° C. and a second dynamic viscosity of less than about 100 cP at a shear rate of 1,000 sec⁻¹ measured at 25° C.; wherein the cosmetic ink composition has a tan(delta) of from about 0.01 to about
 1. 2. The cosmetic ink composition of claim 1 wherein the cosmetic ink composition comprises a ratio of (meth)acrylic acid homopolymer or salt thereof to rheology modifier of from about 0.10 to about 0.75.
 3. The cosmetic ink composition of claim 1 wherein the cosmetic ink composition has a neat pH of from about 7.5 to about 9.0.
 4. The cosmetic ink composition of claim 1 wherein the particulate material has a Particle Size Distribution D50 of about 100 nm to about 2,000 nm.
 5. The cosmetic ink composition of claim 1, wherein the particulate material has a Particle Size Distribution D50 of from about 200 nm to about 350 nm.
 6. The cosmetic ink composition of claim 1, wherein the particulate material has a Particle Size Distribution D90 of from about 700 nm to about 900 nm.
 7. The cosmetic ink composition of claim 1 wherein the cosmetic ink composition comprises from about 0.01 to about 1 active wt % of the (meth)acrylic acid homopolymer or salt thereof.
 8. The cosmetic ink composition of claim 1 wherein the (meth)acrylic acid homopolymer or salt thereof is sodium polyacrylate.
 9. The cosmetic ink composition of claim 1 wherein the particulate material comprises a metal oxide.
 10. The cosmetic ink composition of claim 9 wherein the particulate material comprises titanium dioxide.
 11. The cosmetic ink composition of claim 10 wherein the titanium dioxide is substantially coated with a coating ingredient selected from silica, alumina, and combinations thereof.
 12. The cosmetic ink composition of claim 1 wherein the (meth)acrylic acid homopolymer or salt thereof has a weight average molecular weight of less than about 20,000 daltons.
 13. The cosmetic ink composition of claim 12 wherein the (meth)acrylic acid homopolymer or salt thereof has a weight average molecular weight of from about 2,000 to about 5,000 daltons.
 14. The cosmetic ink composition of claim 1 further comprising one or more skin care actives selected from the group consisting of niacinamide, inositol, undecylenoyl phenylalanine, and combinations thereof.
 15. The cosmetic ink composition of claim 1 further comprising a preservative.
 16. The cosmetic ink composition of claim 1 further comprises from about 20 to about 30 active wt % of a humectant. 